Coaxial Stub Filtering

[KWIDELITZ at delphi.com]

I want to use coaxial stubs to trap out interference in a two radio
setup. I've got a Dunestar Bandpass filter in
line with Radio B, which works some, but with some combinations
of transmitting on certain bands and with certain antennas on Radio A
and listening on certain bands/using certain antennas on Radio B, it
doesn't do the trick satifactorily. I want to add coaxial stubs for
additional attentuation. My idea is to use an automatic antenna
switch setup to get the band Radio A is on, and switch in a stub
Tee'd of the Radio B line. My understanding is that each stub is
a quarter wave piece of coax. Is there a problem with harmonics
on the stubs? For instance, if Radio A is on 40 and Radio B is on
15, will the 40 meter stub absorb some of the 15 meter transmitted
signal? Can the stub be coiled up? Can I use RG-58 for the stub? All
my transmission lines are RG-213. Does it matter how far from Radio B
the stubs get Tee'd in? I saw a note about using trimmer capacitors
at the end to tune the stubs. What values are suggested and what
technique to tune? Thanks for your help. 73. Ken, AB6FO.

>From raid5!davep at csn.org (Dave Palmer)  Wed Nov 10 23:42:25 1993
From: raid5!davep at csn.org (Dave Palmer) (Dave Palmer)
Date: Wed, 10 Nov 93 16:42:25 MST
Subject: N6KL SS CW Single Op results
Message-ID: <9311102342.AA26214 at raid5>


N6KL results from Colorado, and advice sought!

  SS CW  Low Power
  304 Qs x 70 Sections = 42,560  16 hours

  80   71   W3EDP-style 3/8 wave-long wire up 20'
  40   80   Inverted Vee up 20' in a tree.
  20   69   AEA Isoloop inside the attic
  15   83     "
  10    1     "

  Low budget station details:   Rig=Ten Tec 544,
  PC=IBM PC Convertible @4.77 MHz, with DoubleDOS and running
  KJ6K's Ultimate CW program in one partition and my "QRR" logging
  program in the other.

  Well that was fun, kinda, but I am beginning to think fun is
  proportional to antenna height.   Overall I did a bit better last year
  portable from Wyoming (won 1st place low power there) and sounds like
  some of you could have used the Wyoming mult.

  The IsoLoop actually works pretty well from inside the attic, but
  snow was still covering the North side of the roof.  For S&P operation,
  the IsoLoop is kind of a pain but you get good at retuning it with
  practice.  On the bands it covered, it was always better than the
  low, outside end-fed wire, except for working other Colorado-ans.

  I had also put an inductively loaded dipole, fed with 450-ohm ladder
  line, inside the attic, but never used it because the outdoor (lower)
  40-meter dipole would receive signals about 10 dB louder!

  I need to call CQ more, even with the lousy antennas.  When I call CQ
  it takes *so* long to get responses, that I get itchy, and feel like
  if I'm not turning the VFO, I'm not doing anything!

  From my CC&R'd QTH, towers are out of the question, so I am left with
  indoor and outside TEMPORARY antennas, so question for you all:

  For domestic contests, which is superior:

  1)  A ground mounted vertical (like HF6V) with large number of radials
  2)  A 2nd-floor balcony-mounted vertical with wire mesh covering the wooden
        balcony, plus a few longer radials wrapping around the house.
        (Balcony is on the south side of the house, so there
        would be some blockage of signals to the north).
  3)  A 200' end fed wire from the 2nd floor out out to a temporary pole
      25' high, wire pointing southwest or southeast.
  4)  Use 30' high metal chimney as support and ground leg for 1/4 wave
      slopers for 40 & 80.
  5)  Mount the IsoLoop on back of the 4x4 and drive to Wyoming and
      operate mobile from quasi-rare section.   :o)

  MANY thanks for any suggestions.   I think there are a lot of us struggling
  weak-signal types who would benefit from you experts out there.  And your
  typical want-to-be contester doesn't *yet* have the big towers, so when
  he/she dabbles in their first couple of events, they get pretty frustrated
  and go do something else.

  73,
  Dave Palmer, N6KL
  davep at arraytech.com     Boulder, CO

>From robert penneys <penneys at freezer.cns.udel.edu>  Thu Nov 11 00:38:59 1993
From: robert penneys <penneys at freezer.cns.udel.edu> (robert penneys)
Date: Wed, 10 Nov 93 19:38:59 EST
Subject: SS score
Message-ID: <9311110038.AA26330 at freezer.cns.udel.edu>


Low power, single op part time effort from Delaware...

567 x 76 = 86,184

Nex year, DXpedition to VE8. Send your $$ here.   

Tnx for Q's, gang. CU on phone, maybe. Bob WN3K   GO FRC!!